This invention relates to the use of optical fibers, and, more particularly, to an adhesive that is used in removably fixing optical fibers onto a payout bobbin in forming a canister.
Optical fibers are strands of glass fiber processed so that light beams transmitted therethrough are subject to total internal reflection. A large fraction of the incident intensity of light directed into the fiber is received at the other end of the fiber, even though the fiber may be hundreds of meters long. Optical fibers have shown great promise in communications applications, because a high density of information may be carried along the fiber and because the quality of the signal is less subject to external interferences of various types than are electrical signals carried on metallic wires. Moreover, the glass fibers are light in weight and made from a highly plentiful substance, silicon dioxide.
Glass fibers are typically fabricated by preparing a preform of glasses of two different optical indices of refraction, one inside the other, or a single glass composition with a coating that ensures total internal reflection, and then processing the preform to a fiber by drawing, extruding, or other process. The optical fiber is then coated with a polymer layer termed a buffer to protect the glass from scratching or other damage. As an example of the dimensions, in a typical configuration the diameter of the glass optical fiber is about 125 micrometers, and the diameter of the fiber plus the polymer buffer is about 250 micrometers.
For such very fine fibers, the handling of the optical fiber to avoid damage that might reduce its light transmission properties becomes an important consideration. The fibers are typically wound onto a cylindrical or tapered cylindrical bobbin with many turns adjacent to each other in a side by side fashion. After one layer is complete, another layer of fiber is laid on top of the first layer, and so on. The final assembly of the bobbin and the wound layers of fiber is termed a canister. At a later time when the optical fiber is to be used, the fiber is ordinarily paid out from the canister in an unwinding operation.
It has been found by experience that, where the fiber is to be paid out from the canister in a rapid fashion, the turns of optical fiber must be held in place on the canister with an adhesive. The adhesive holds each turn of fiber in place as adjacent turns and layers are initially wound onto the canister, and also as adjacent turns and layers are paid out. Without the use of an adhesive, payout of the fibers may not be uniform and regular, leading to snarls or snags of the fibers that damage them or cause them to break as they are paid out.
The currently used optical fiber adhesive is a neoprene adhesive that is applied to the turns of optical fiber in a discontinuous fashion. That is, after a layer is wound onto the canister, the winding operation is stopped, and the adhesive is sprayed onto the layer. After a brief pause to permit the adhesive to dry, the next layer is wound overlying the layer to which the adhesive was applied. The discontinuous winding operation slows the production of wound fiber optical canisters. There is reason to believe that the neoprene adhesive application process induces surface changes to the optical fiber that increases the optical loss from the fiber during subsequent use. The optical loss is a serious drawback of the neoprene adhesive. The relatively high glass transition temperature of the neoprene adhesive causes it to become brittle when cooled, leading to possible cracking of the adhesive that can cause difficulties during fiber payout. The neoprene can oxidize during elevated temperature exposure, also leading to brittleness.
There is a need for an improved adhesive for use in optical fiber winding and payout operations. Such adhesive should have the necessary mechanical properties to ensure a uniformly wound canister, should not cause damage to the light transmission properties of the optical fiber, and should promote uniform payout of the optical fiber even after prolonged storage at extreme temperatures. The present invention fulfills this need, and further provides related advantages.